1. Changes in Ecosystems: Ecological Succession

2. Ecological Succession
Ecosystems are constantly changing in response to natural and human disturbances.
As an ecosystem changes, older inhabitants gradually die out and new organisms move in, causing further changes in the community.
Ecological Succession – Series of predictable changes that occurs in a community over time

3. Some Causes of Ecological Succession
Can result from slow changes in the physical environment or from sudden disturbances (either natural or man made).
Some causes include:
Clearing land
Climate change
Introduction of nonnative species
Natural disasters such as volcanic eruptions, forest fires, hurricanes, & floods

4. Succession:
Natural, gradual changes in the types of species that live in an area; can be primary or secondary
The gradual replacement of one plant community by another through natural processes over time

5. Primary Succession Begins in a place without any soil
Sides of volcanoes
Landslides
Flooding
Starts with the arrival of living things such as lichens that do not need soil to survive
Called PIONEER SPECIES

7. Primary Succession
Soil starts to form as lichens and the forces of weather and erosion help break down rocks into smaller pieces
When lichens die, they decompose, adding small amounts of organic matter to the rock to make soil

9. Primary Succession
Simple plants like mosses and ferns can grow in the new soil

10. Primary Succession The simple plants die, adding more organic material
The soil layer thickens, and grasses, wildflowers, and other plants begin to take over

11. Primary Succession
These plants die, and they add more nutrients to the soil
Shrubs and tress can survive now

12. Primary Succession
Insects, small birds, and mammals have begun to move in
What was once bare rock now supports a variety of life

13. Mount St. Helen Before Eruption in 1980

14. Mount St. Helen After Eruption
Mount St. Helen 6 Years After Eruption
Mount St. Helen 10 Years After Eruption
Mount St. Helen 19 Years After Eruption

15. Secondary Succession
Begins in a place that already has soil and was once the home of living organisms
A disturbance of some kind changes an existing community
Occurs faster and has different pioneer species than primary succession
Example: after forest fires

18. Climax Community
A stable group of plants and animals that is the end result of the succession process
Does not always mean big trees
Grasses in prairies
Cacti in deserts